Local surface photo-voltage imaging, using a scanning tunnelling microscope, was used to demonstrate 2 types of local Fermi-level pinning next to a single adsorbate or defect. Advantage was taken of tip-induced band-bending due to the lack of gap states at clean (110) surfaces. The pinning energy at a single Cs adatom location was deduced to be 0.56eV above the valence-band maximum. In the case of As, the Fermi level could not go below the top of a filled surface state; 0.62eV above the valence-band maximum.

Local Fermi-Level Pinning at a Single Adatom (Cs) or Vacancy (As) on a GaAs(110) Surface S.Aloni, I.Nevo, G.Haase: Physical Review B, 1999, 60[4], R2165-8